A nuclear RTG works by utilizing the waste heat generated by the radioactive decay of plutonium-238. This not only has a half-life of 87.7 years, but it also generates a very respectable 560 watts of energy per kilogram per second [...]
Sigh!
A watt is not a unit of energy, but rather of power. And a Radioisotope Thermoelectric Generator (RTG) is already nuclear - so there's no need to repeat that word in describing one.
To be brief: An RTG produces 560 watts of power per kg.
Regards,
To be briefer: An RTG produces 560 watts per kg.